The present invention relates to a new and improved process for the continuous bonding of staple fibers into a stable band and to a new and improved stable band produced according to the aforementioned inventive process.
The textile spinning art is already acquainted with the technique of forming stable bands from staple fibers by adhesive bonding. According to this known process a suitable prepared, nontwisted staple fiber arrangement is imbued with an excess of a liquid having distributed therein an adhesive, the excess liquid is squeezed off in a pressure zone while compacting at all sides the staple fiber arrangement into a band, and the staple fibers compacted into the band are transformed into a stable band by setting the adhesive. In the most simple manner the adhesive is set by drying same by means of dry air at temperatures which are conventionally employed in drying techniques. In this regard attention is invited to my U.S. Pat. No. 3,548,462, granted Dec. 22, 1970.
When applying the liquid by means of a liquid applicator device, for instance of the type disclosed in Swiss Pat. No. 426,704 or my U.S. Pat. No. 3,426,389, the staple fibers which are extensively parallely oriented at the fiber arrangement are strongly compacted or compressed together at the pressure zone and between work disks are compressed together to a minimum spacing x. Still it is not possible to prevent that, after departure of the fiber band from the pressure zone, such immediately again expands to amount y which can constitute a multiple of the aforementioned value x. This cross-sectional expansion of the band is dependent, for instance, upon the fiber material, the degree of crimping of the fibers, the viscosity of the liquid and other similar factors, but in any case even under the most favorable conditions this phenomenon is always present.
This expansion of the fiber band after departure from the pressure zone, particularly in the case of hydrophilic staple fibers, together with the swelling of the fibers which begins following application of the liquid, constitutes a decisive drawback. Such is known to those skilled in the art as the so-called "sandwich-effect" and occurs because of an evacuation of liquid at the outermost cover layer or skin of the band. In other words the liquid introduced into the band and originally uniformly distributed migrates from the cover or outer layer of the band towards the core of the band, internally thereof brings about an increased concentration of liquid, which equally affects the adhesive distributed in the liquid. This sandwich effect is especially then still further intensified if it is simultaneously desired to maintain as short as possible the time between application of the liquid to the staple fibers and drying of the band, whereby the dimensions of the installation can be reduced in a very favorable manner.
After setting of the adhesive or drying there is thus obtained a stable band with only an insufficiently bonded cover or outer layer, so that a subsequent orderly drafting in a singlezone drafting arrangement becomes questionable. Furthermore, owing to break-out of entire parts of the cover layer there can result unusable products having numerous thickened locations.
With the known process, particularly further imparied by the "sandwich-effect", it has been found that the adhesion force of the adhesive distributed in the liquid can only be unsatisfactorily utilized, resulting in considerably economical disadvantages.